增强for循环

它的底层实现就是使用Iterator。
     什么样的容器可以使用增强for？-----------实现Iterable接口
     
     增强for的缺点:只能进行遍历，不能进行在遍历过程中的操作.
     
     增强for的格式
      for(类型 引用:容器){
      }

关于对集合的遍历.

 

 1 package com.hexiaolin.work;
 2 
 3 import java.util.ArrayList;
 4 import java.util.HashMap;
 5 import java.util.HashSet;
 6 import java.util.Iterator;
 7 import java.util.List;
 8 import java.util.ListIterator;
 9 import java.util.Map;
10 import java.util.Set;
11 
12 import org.junit.Test;
13 
14 public class ConnDemo {
15     //集合list的遍历
16     @Test
17     public void list() {
18         List<Integer> list = new ArrayList<Integer>();
19         for (int i = 0; i < 10; i++) {
20             list.add(i);
21         }
22         
23         //1 Iterator迭代器
24         for (Iterator<Integer> iterator = list.iterator(); iterator.hasNext();) {
25             System.out.println(iterator.next());
26         }
27         System.out.println("##############");
28         
29         //2 ListIterator 
30         for (ListIterator<Integer> iterator =list.listIterator(); iterator.hasNext();) {
31             System.out.println(iterator.next());
32         }
33         System.out.println("##############");
34         //3普通for
35         for (int i = 0; i < list.size(); i++) {
36             System.out.println(list.get(i));
37         }
38         System.out.println("##############");
39         //4Iterator迭代器+while循环
40         Iterator< Integer> iterator=list.iterator();
41         while (iterator.hasNext()) {
42             System.out.println(iterator.next());
43         }
44         System.out.println("##############");
45         //5增强for
46         for (Integer integer : list) {
47             System.out.println(integer);
48         }
49         System.out.println("##############");
50     }
51     //集合Set的遍历
52     @Test
53     public void set() {
54         Set<Integer> set=new HashSet<Integer>();
55         for (int i = 0; i < 10; i++) {
56             set.add(i);
57         }
58         //Iterator迭代器
59         for (Iterator<Integer > iterator = set.iterator();iterator.hasNext();) {
60             System.out.println(iterator.next());
61         }
62         System.out.println("##############");
63         //增强for
64         for (Integer integer:set) {
65             System.out.println(integer);
66         }
67         System.out.println("##############");
68     }
69     //集合Map的遍历
70     @Test
71     public void map() {
72         Map<String, String> map=new HashMap<String, String>();
73         for (int i = 0; i < 10; i++) {
74             map.put("key"+i, "value"+i);
75         }
76         //keySet
77         for (String key :map.keySet()) {
78             System.out.println(key+"  "+map.get(key));
79         }
80         System.out.println("##############");
81         //entrySet
82         for (Map.Entry<String, String> entry :map.entrySet()) {
83             System.out.println(entry.getKey()+"  "+entry.getValue());
84         }
85         System.out.println("##############");
86     }
87 }

 

转载于:https://www.cnblogs.com/junfeng930512/p/3512920.html